Nov., 1951
EXCHANGE REACTIONS OF 4-COORDINATED [CONTRIBUTION FROM
THE
CHEMISTRY DEPARTMENT OF
THE
NICKELCOMPLEXES
5419
UNIVERSITY OF WISCONSIN]
Exchange Reactions of Some 4-Coordinated Nickel Complexes BY NORRISF.HALLAND BENNETTR.WILLEFORD, JR.’~~ We have studied the exchange reactions of fourteen 4-coordinated nickel complexes of various types using labeled nickel chloride in solution a t room temperature. The exchange results are correlated with published magnetic susceptibilities and other measurements indicative of the types of bonds present. All four of the compounds which are paramagnetic in the solid state exchanged readily. Five of the diamagnetic complexes did not exchange, while five others did. Ethylenediamine, as contrasted with its higher homologs, confers special inertness on certain complexes containing it. A previous correlation between rate of nickel exchange and rate of nickel precipitation with dimethylglyoxime is confirmed and extended. A comparison is made of the rate of exchange of the central atom in certain complexes of copper and of nickel.
While no completely general relation is to be expected between the strength or nature of bonds in compounds and their rates of isotopic exchange, many special correlations of this type are well established.”-B I n particular Johnson and Hall,7 who studied nickel complexes in solution, report “in the main . . . a satisfactory correlation (of exchange rates) with predictions of bond type based on other criteria.” The purpose of the present work was to survey the exchange behavior of some additional 4-coordinated nickel complexes and if possible to define more clearly the relationships between bond type and exchangeability of the central atom. Experimental Radioactive Nickel.-The radionickel used was obtained from the Isotopes Division, U. S. Atomic Energy Commission at Oak Ridge. It is probably a mixture of NP3 and Both of these isotopes are long lived and give off principally very soft radiation.8 In this paper the radionickel will be referred t o as NP3, since this apparently is the predominant isotope. As received from Oak Ridge, the radionickel was contaminated by eo@. This was removed by adding cobalt carrier and precipitating the nickel with dimethylglyoxime. Three or four precipitations were usually sufficient to reduce the cobalt activity to a level which could not interfere with the counting of the radionickel. Exchange Procedure.-A quantity of the nickel complex was dissolved in a suitable solvent, usually pyridine or methyl cellosolve. Since the complexes were slightly soluble, a nearly saturated solution was generally used, and in most cases the concentration was close to 10-*M. Approximately equivalent amounts of the solution of the complex and of a methyl cellosolve solution of radioactive nickel chloride were mixed and shaken mechanically at room temperature. After an appropriate time, the complex was separated from the salt. This was accomplished either by pouring the exchange solution into ice water to precipitate the complex, or by adding chloroform and water and extracting repeatedly, the nickel chloride going into the aqueous phase and the complex into the chloroform phase. The nickel chloride solution was evaporated t o dryness to get rid of the organic solvent and the residue was taken up in sulfuric acid. The acid was neutralized, a large excess of ammonia added, and the nickel removed by electrolysis. If the complex was in chloroform solution, the organic solvent was evaporated. The complex was then treated with nitric acid and this solution was evaporated to dryness. The residue was taken up in sulfuric acid and heated. If the complex had been pre-
cipitated and filtered, it was destroyed with nitric acid, the solution was evaporated to dryness, and sulfuric acid added and heated. At this point, in either procedure, the solution was neutralized, an excess of aqueous ammonia added and the solution electrolyzed to remove the nickel. The nickel was electroplated onto a weighed platinum foil electrode approximately 4 X 4 cm. in size. The washed electrode was then reweighed to determine the weight of the nickel. All weighings were made on a microbalance. The electrode was placed inside the ionization chamber of a Lauritsen electrode and the rate of discharge of the electroscope was measured and expressed as scale divisions per minute. The counting rate was then corrected for the background discharge rate of the electroscope. This corrected counting rate was divided by the weight of the nickel to give the specific activity of the nickel in the given fraction. In only five cases did the weight of the nickel deposit exceed 100 micrograms per sq. cm., and of these the greatest was 242 pg. cm.-2. In 35 cases the deposit weighed less than 100 pg. cm. -z. At these thicknesses self-absorption should not affect the specific activity within the error of the measurement If no exchange occurs the specific activity of the nickel chloride fraction is equal to that of the original radionickel, while that of the complex fraction is essentially zero. If complete exchange occurs, the specific activities of the two fractions are equal. In other cases the extent of exchange is measured by the ratio of the specific activity of the complex to the specific activity for complete exchange calculated from the relative weights of the two types of nickel used. Solvents.-Methyl cellosolve is an effective solvent for most of these complexes and for simple nickel salts. Since pyridine, like ammonia, forms quite stable Complexes with nickel ion, it may be expected7.9 to modify the exchange behavior of a complex more than methylcellosolve. It is also almost the only common organic solvent known to dissolve certain of the complexes. In the pyridine experiments, a mixed solvent was used for convenience, since the radionickel chloride was already in methyl cellosolve solution. Analysis of Compounds.-All the complex salts were analyzed for nickel by the dimethylglyoxime method except that in the cases of compounds 10, 14 and 15 the residue from the carbon and hydrogen determinations was weighed and assumed t o be NiO. Compounds no. 6, 7 and 14 were analyzed for C and H by the Clark Microanalytical Laboratory, Urbana, Illinois, all the others by the microanalytical laboratory of this Department. The correspondence between the analytical results calculated and found was satisfactory in all cases.
Results
The complexes studied are arranged in four groups in Table I. Some of Johnson and Hall’s results are included for comparison. In the column headed Solvent, “Mecel, Etcel, Acet.” and “Pyr.”stand for methyl and ethyl cello(1) Atomic Energy Commission Fellow, 1949-1950. solve, acetone, and a 7-3 mixture of pyridine and methyl (2) Department of Chemistry, Bucknell University, Lewisburg, cellosolve, respectively. Under Separation method, “P” Pennsylvania. means precipitation by dilution with ice-water and “E” (3) N F. Hall and 0.R. Alexander, THIS JOURNAL, 62, 3455 (1940). extraction into chloroform. (4) Chcm. SOC.London Ann. Rcgorts, 88, 89 (1941). (5) M.Haissinsky J . chim. phys., 4T, 957 (1950). (6) C. S. Garner, “Applications of Exchange Reactions in Studying
Lability” (paper presented at the Symposium on Equilibrium and Rate Behavior of Complex Ions in Solution), Chicago, Ill., February 21, 1951. (7) J. E.Johnson and N. F. Hall, TPZSJoawbb, 7 4 2344 (1948). (8) A. R. Brosi, J. Borkowaki, R. E. b n n nnd J. C. Clriess, fr., phyt. 11,aei ( 1 9 ~ ) .
m.,
e.
Discussion Group. I. 1. Bis-(salicyla1dehydo)-nickel.Studied by Johnson and Hall.’ Paramagnetic both in the“so1id statelo and in pyridine solution? (8) J. B. WilllS snd D. P. Mellm, T E IJ~O W R ~ ~ A L8, , 1237 (i947), (IO) 0. N.Tyson and 5.C. Adama, ibid., 69, 1228 (1940).
54.20
KORKIS17. HALLAND BENNETTI
